Current knowledge on the cellular energetics of heat production is based primarily upon experimental measurement of basal and active heat production in muscle tissue. The quality of myothermal measurements to date, rest largely upon the resolution and accuracy of a sensitive thermopile and critically damped mirror-galvanometer system first introduced in 1951. Although minor improvements have accrued since then, many theoretical and experimental limitations dictate the accuracy of the data obtained, and limit the types of experiments that are feasible. This proposal outlines a new physical approach for myothermal measurements based upon the thermal-optical behavior of various cholesteric liquid crystals which represent the ultimate in temperature detection. By measuring the intensity of selectively reflected light at constant wavelength, accurate heat quantities can be accessed, down to the level of "temperature noise" in the system. Year I goals include the completion of a prototype system, evaluating system parameters, and calibration of the thermal response in terms of sensitivity and temporal resolution. Year II goals include a detailed comparison of frog sartorii isometric heat production measurements with those previously reported in the literature; special interest will be given to an analysis of the earliest heat production rates; additional shortening heat experiments are also planned. Year III, utilizing microencapsulted liquid crystals in conjunction with single, large myofibers of Balanus sp., is to be devoted to direct, intracellular heat production studies on isometric preparations. Future work using liquid crystal thermography appears limitless and generally applicable to many cellular thermal measurement problems.